As @A.B. said, the files don't have a CreateDate. If these files are from a camera, then the tag you probably want to use instead is DateTimeOriginal, which is set by nearly all cameras.
Try this command:exiftool -time:all --system:all -s
This will show you all the time tags (but not the file system timestamps) in your file and from there you can figure out what is the best tag to use for your command.
